Craigslist help please?

I was selling my couches on Craigslist and a person wanted to buy them from Philadelphia (I'm from chicago) they sent me a check for the price of the couches and said they would take care of the shipping. Everything was fine I got the check, but never deposited into my account. A personal problem came up so I won't be able to sell them anymore and I told them that. I told them I still had the check and asked if they could send me their address so I can send them the check back. So they said I should still deposit it into my account and send them another check, which I'm not going to do because it's pointless. I told them that and then they told me that I'm lying and that they checked their account and it says I have taken the money and they will call the cops if I don't give the, their money back. I don't understand any of this because I still have the check and I'm not afraid of them calling the cops because I know I haven't taken their money.